In recent years, due to the high cost of fuel and the need for energy conservation, the long established standing pilot for gas fired burner equipment has decreased in favor. In some states the use of standing pilots for gas fired equipment has been restricted or eliminated by statute. The conventional standing pilot was an exceedingly inexpensive and safe type of device when the pilot was linked to its related gas valve by a simple pilot safety system.
The conventional standing pilot for gas fired equipment has been replaced by intermittent pilot systems utilizing a spark generator to ignite a pilot flame, which in turn is used to ignite the main burner. This type of equipment typically relies on a spark generator and two sequentially opened gas valves. The smaller of the gas valves is normally referred to as the pilot valve and provides a fuel to a pilot burner which is ignited by a spark source. The spark source can be a small, high voltage alternating current transformer, or more typically is a relaxation type of oscillator utilizing a silicon controlled rectifier, capacitor and step-up transformer. Once the pilot has been ignited, a flame sensor allows for the energization of a main valve solenoid which then supplies fuel gas to the main burner. The main burner is then ignited from the pilot. This type of equipment, normally electronic in nature, is subject to many types of failures. As a result of this, a great deal of design effort has been expended in producing solid state control systems and spark generators which have a high degree of safety and reliability. Most of the equipment of this type has relied upon redundant electronics, and static safe start check operations of the electromechanical relays which are normally used for control of the pilot valve and the main gas valve.